At an average moment how many planes, worldwide, are airborne and how many people are travelling in them?

It's a lot. Boeing used to advertise that a Boeing jet is taking off or landing somewhere in the world every two seconds. We can assume then that a minimum of one flight per second starts somewhere in the world. At an average of 100 passengers per flight, we have 360,000 passengers aloft per hour, if flights average one hour at least. If we allow for Eastern Bloc countries, turboprops and GA aircraft, this figure could well triple. That would put the number of people in the air at any one time at over a million.